Miscible displacement oil recovery process



May 27, 1969 C. E. COOKE, JR

MISCIBLE DISPLACEMENT OIL RECOVERY PROCESS Filed Oct. 27, 1966 DETERGENTI PHASE PHASE POLAR ORGANIC SODIUM XYLENE SULFONATE SODIUM CUMENESULFONATE TERT AMYL ALCOHOL ALKYL BENZENE SULFONATES SEC BUTYL ALCOHOL 8I2% TALL OIL PITCH WATER PENTANOIC ACID FIG 4 CLAUDE E. COOKE, JR.INVENTOR.

A T TORNE Y United States Patent U.S. Cl. 166-274 6 Claims ABSTRACT OFTHE DISCLOSURE In the recovery of oil from subterranean oil-bearingformations, a polar organic solvent is injected into the formation. Thepolar organic solvent is followed by an aqueous detergent solutionhaving a detergent concentration which is, at least, the minimummiscibility concentration in a system of aqueous liquid, polar organicsolvent, and detergent. The polar organic solvent and detergent solutionare displaced into the reservoir and oil is recovered from theformation. The volume of injected solvent should be about 3 percent to20 percent of the pore volume of the reservoir to be flooded and thevolume of aqueous detergent solution injected should be about 3 percentto 20 percent of the pore volume of the reservoir to be flooded.

Cross reference to related application This application is acontinuation-in-part of U.S. application Ser. No. 507,836 of Claude E.Cooke, Jr., filed Nov. 15, 1965 now U.S. Patent No. 3,373,809.

Summary of the invention This invention relates to the recovery of oilfrom natural subsurface reservoirs. A method is provided for themiscible displacement of reservoir oil by injecting a bank of polarorganic solvent into the reservoir, followed by injecting an aqueousdetergent solution to displace the polar organic solvent and the oiltoward one or more recovery wells.

It is generally recognized that a polar organic solvent can be readilyselected which is completely miscible with crude petroleum, and thatefficient recovery of the crude can be achieved by displacing such asolvent through a reservoir. It is also known, hypothetically, that ifsuch a solvent were also miscible with water, it could be efficientlyand economically displaced through a reservoir by the injection ofordinary flood Water.

The concept of such an ideal solvent has remained hypothetical, at leastfor some crude oils. Recent efforts have therefore sought to provide atleast two successively injected solvent banks: (1) a leading bankcapable of miscibly displacing the reservoir crude, and (2) a solventhaving mutual miscibility with both the leading bank and with water. Forexample, it has been proposed in the literature to inject a leading bankof amyl alcohol, selected because of its miscibility with petroleum,followed by a bank of ethyl alcohol, selected because of its miscibilitywith both amyl alcohol and with ordinary flood water. Such injection oftwo solvent banks would in fact permit the reservoir oil and eachsolvent bank to be miscibly displaced, if the process were applied to asubstantially water-free reservoir, and if mixing of the solvents withthe driving water were negligible. But the presence of substantial watersaturations in most reservoirs, and especially in a previouslywaterfiooded reservoir, leads to serious complications. For example,when injecting amyl alcohol followed by ethyl alcohol, followed byWater, true miscible displacement of the amyl alcohol generally cannotoccur because the ethyl alcohol, upon substantial dilution by water, isno longer sufficiently miscible with amyl alcohol.

On the other hand, if an alcohol having greater water solubility wereselected to replace the amyl alcohol as a leading bank, in order toensure its miscible displacement by ethyl alcohol, then water dilutionof the leading bank would cause a loss of its ability to misciblydisplace the reservoir oil. Perhaps if the amyl alcohol were followed bybutyl alcohol, then by propyl alcohol, then by ethyl alcohol, and thenby water, the reservoir oil and each alcohol bank would be misciblydisplaced. However, eco nomic considerations make it impractical toinject as many as three or more solvent banks.

Prior attempts to achieve miscible displacement of the crude petroleum,followed by miscible displacement of each succeeding solvent bank, havegenerally contemplated true molecular dissolution of the displaced phaseby the displacing medium. The present invention, however, overcomes thedifliculties normally arising from dilution with reservoir water by theinjection of a polar organic solvent which, in equilibrium with water,is capable of miscibly displacing the reservoir crude, followed by theinjection of an aqueous detergent solution capable of misciblydisplacing the solvent bank by micellar solubilization or hydrotropy.

In accordance with a particular embodiment, the polar organic solventinjected in accordance with the invention contains a thickening agent.This embodiment is particularly useful when recovering a petroleum crudeof greater viscosity than the polar organic solvent. A suitablethickening agent is selected from various natural and syntheticthickening compositions having a sufficient solubility in the polarorganic bank to increase its viscosity. Any substantial increase inviscosity is beneficial; however, it is preferred to thicken the polarorganic bank to a viscosity at least substantially equal to theviscosity of the reservoir oil. Examples of suitable thickened polarorganic solvent banks include secondary butyl alcohol thickened withethyl cellulose, tertiary amyl alcohol thickened with polyvinyl alcohol,tertiary octyl amine thickened with polyacrylic acid, and tertiary amylalcohol thickened with polystyrene.

Other additives or auxiliary solvents may be blended With the polarorganic bank. For example, about 5 percent to 30 percent by volume ofcarbon dioxide blended with an alcohol bank, or other polar organic, isgenerally useful to increase the miscibility of the alcohol withpetroleum, and to reduce the cost of the solvent bank. Lighthydrocarbons, such as toluene or LPG, are also useful for this purpose.

In accordance with a further embodiment, the aqueous detergent solutioninjected in accordance with the invention contains a thickening agent.The use of a thickening agent in the detergent bank is generally usefulwhen the mobility of the polar organic bank is less than the mobility ofthe detergent bank. (Mobility is the ratio of permeability to viscosity,and is a measure of the ease with which a fluid flows through apermeable formation.) Certain polar organic solvents have a viscositygreater than the viscosity of the typical detergent solution to beinjected for displacing the polar organic bank. In other instances, thepolar organic bank will be more viscous than the detergent solution as aresult of adding a thickener.

It is preferred to include a suflicient concentration of thickeningagent to increase the viscosity of the detergent solution to a value atleast substantially equal to the viscosity of the solvent bank. Suitablethickened detergent solutions include xylene sulfonate and apolysaccharide polymer, xylene sulfonate and partially hydrolyzedpolyacrylamide, and a sulfonated light aromatic refinery stream and apolysaccharide polymer.

It is also contemplated that a thickening agent will sometimes bedesirable in the flood water injected to displace the detergent bank.Thus in some instances it may be desirable to thicken each of thevarious liquids injected in accordance with the invention, in order toprovide a favorable mobility ratio between the reservoir oil and thesolvent bank; between the solvent bank and the detergent bank; andbetween the detergent bank and the fiood water subsequently injected topropel or displace the successive banks toward one or more recoverywells.

In accordance with a further embodiment, the mobility of the polarorganic bank is reduced by the concurrent or intermittent injection ofwater or brine therewith. Similarly, the mobility of either the solventbank or the detergent bank, or both, may be reduced by the concurrent orintermittent injection of an inert, immiscible gas.

FIGURE 1 is a ternary phase diagram illustrating the concentration ofdetergent in water required to obtain miscible displacement of a polarorganic solvent bank.

FIGURE 2 is a ternary phase diagram for the tertiary amylalcohol-brine-sodium cumene sulfonate system.

FIGURE 3 is a ternary phase diagram of a system comprising secondarybutyl alcohol and tall oil pitch, brine, and sodium xylene sulfonate.

FIGURE 4 is a ternary phase diagram showing the twophase envelopes ofthe pentanoic acid-water-alkyl benzene sulfonate system, and thepentanoic acid-brine-alkyl benzene sulfonate system.

The polar organic solvent injected in accordance with the invention isnot mutually miscible with both water and the reservoir oil. Theanhydrous solvent is completely miscible with most petroleum crudes, buthas only a limited solubility in water; and is capable of dissolvingonly a limited amount of water. An essential characteristic of thesolvent is its ability to retain substantial miscibility with petroleum,even when saturated with reservoir water. A limited amount of asphalticmaterial may be precipitated from the petroleum, but this occurrence isimmaterial in the miscible displacement of the liquid petroleumhydrocarbons by the polar organic solvent.

It is also within the scope of the invention to inject a polar solvent'which is substantially completely immiscible with water. Normalhexanol, for example, is less than 1 percent Water-soluble but is farmore readily solubilized by an aqueous detergent solution than is crudepetroleum. A second essential characteristic of the solvent, in additionto its capability of miscibly displacing the reservoir hydrocarbons, isthat it be more readily solubilized by an aqueous detergent solutionthan is the reservoir oil.

The flow behavior of a polar organic solvent bank in a porous, permeablereservoir, and the mechanism by which it miscibly displaces thereservoir oil has been the subject of several prior disclosures.Miscible displacement is generally recognized as a preferred mechanismof oil recovery, in order that on a pore volume basis much smaller, moreeconomical banks of injected solution can be employed to obtain maximumoil recovery.

It has now been found that a polar organic solvent which issubstantially immiscible with water can itself be efliciently recovered,in a manner closely analogous to miscible displacement, by injecting anaqueous detergent solution, preferably followed by ordinary water orbrine. The flow behavior and the mechanism by which the solvent isdisplaced resembles true miscible displacement in that the detergentbank carries in aqueous solution certain materials which pass by masstransfer into the solvent phase, thereby increasing its volume. Inaddition, some portions of residual solvent saturations will becomemobilized because of a lowering of interfacial tension, whereby thesolvent bank is driven ahead of the detergent solution. A substantialportion of the solvent bank is actually solubilized to form awater-continuous microemulsion whereby the detergent solution and thesolubilized solvent are transported through the reservoir at the samevelocity in a manner closely analogous to the flow behavior observed inthe case of true molecular dissolution.

In FIGURE 1 the phase diagram of a hypothetical Water-detergent-polarorganic solvent system is shown. It can be demonstrated that a bank ofthe polar solvent will be miscibly displaced by the injection of anaqueous detergent solution having a detergent concentration greater thanthat concentration represented by the point C in the phase diagram. Thepoint C is defined by the intersection of a line with thewater-detergent side of the diagram, drawn tangent to the two-phaseenvelope at the plait point P. The detergent concentration at point C isreferred to herein as the minimum miscibility concentration.

Note that miscibility in all proportions between the aqueous detergentsolution and the polar organic solvent is not a prerequisite to miscibledisplacement of the solvent. That is, a straight line connecting point Cwith the solvent vertex will usually cut across the two-phase envelope.Therefore, initial mixing of the detergent solution with solventproduces a two-phase composition. Further mixing, however, builds atransition zone miscible with both the detergent solution and thesolvent, which permits true miscible displacement.

Suitable classes of polar organic solvents for use in accordance withthe invention include the normal, secondary, tertiary, cycloandiso-alcohols having 4-16 carbon atoms per molecule; the normal,secondary, tertiary, cycloand iso-amines having 6-12 carbon atoms permolecule; phenol and substituted phenols having side chains with 1-10carbon atoms per molecule; normal, secondary, tertiary, cycloandiso-mercaptans having 2-10 carbon atoms per molecule; fatty acids having5-22 carbon atoms per molecule; ketones having 4-18 carbon atoms permolecule; ethers having 4-18 atoms per molecule; aldehydes having 4-18carbon atoms per molecule; and mixtures of two or more of the abovesolvents. Each of these examples may contain saturated or unsaturatedcarbon-carbon bonds.

The polar organic solvent may be injected as a pure compound or as acrude mixture containing other oxygenated hydrocarbon products, orcontaining inert materials having no detrimental effect upon the abilityof the solvent bank to displace the reservoir oil. The injected solventmay contain water or brine up to the limit of its solubility therein.Solvent recovered at production wells is separated from the oil andreinjected elsewhere in the same reservoir, or in a separate reservoir.

Suitable detergents or surfactants to be injected as aqueous solutionsinclude the anionic and nonionic surface active compounds, includingsulfonated aromatic hydrocarbons, ethylene oxide condensate of aliphaticacids, alkyl aryl polyalkylene glycol ethers, esters of sulfosuccinicacid, mono-and dibasic carboxylic acids, alkyl and aryl sulfates;specific examples of which include isopropyl naphthalene sodiumsulfonate, sulfonated petroleum distillates, ethylene oxide condensatesof coco fatty acids, octylphenyl polyoxethylene ether, diisoctyl sodiumsulfosuccinate, perfluocaprylic acid, diisohexyl succinic acid, dodecylsulfate, and amyl phenyl sulfate, or mixtures of two or more of theabove. Preferred detergents are the alkyl benzene sulfonates having oneto seven alkyl carbons per molecule. Specific examples include cumenesulfonate, amyl toluene sulfonate, xylene sulfonate, and butyl benzenesulfonate. Typically, these detergents are injected as alkali metal orammonium salts; however, the sulfonic acids may be injected as suchwithout neutralization. To some extent, the acids react with thereservoir rock to form salts in situ. The short-chain alkyl benzenesulfonates are far superior to the Well-known long-chain alkyl benzenesulfonates, because of the solubility of their calcium and magnesiumsalts, and their relatively much lower adsorptivity on reservoir rock.

The concentration of detergent or of detergent mixtures useful inaccordance with the present invention lies in the range of about 2percent by weight up to about 40 percent by weight, preferably from 5percent to 25 percent by Weight, based on the total weight of theinjected detergent solution. It will be apparent that theseconcentrations are greater than the concentrations generally proposed inthe prior art for the use of surfactants as waterfiood additives for oilrecovery. The greater concentrations are essential in accordance withthe present invention since the present displacement mechanism involvesa solubilization of the solvent in Water, to achieve miscibledisplacement, whereas the typical prior use of detergents has been tolower interfacial tension Without achieving solubilization or miscibledisplacement. The volume of injected solvent should be about 3 percentto 20 percent of the flooded pore volume of the reservoir. The volume ofthe aqueous detergent solution should also be about 3 percent to 20percent of the flooded pore volume of the reservoir.

Specific examples of suitable polar organic solvents to be injected inaccordance with the invention include normal amyl alcohol, tertiary amylalcohol, normal, secondary, or iso-butyl alcohols, valeric acid,hexanoic acid, or mixtures thereof. In selecting specific mixtures ofsolvents it is frequently desirable to adjust the density of the blendto substantially equal the density of the reservoir oil.

It will be apparent that some of the above-named surfactants ordetergents are sensitive to divalent ions such as calcium and magnesium,frequently encountered in petroleum reservoirs. It is contemplated insuch instances that the detrimental effect of these ions can be avoidedby the addition of a chelating agent to the flood Water or bypreflooding the reservoir to displace divalent saltcontaining brines andthereby avoid the difiiculty.

In the system represented by FIGURE 2, the brine contains about 2.3percent sodium chloride, about 0.3 percent calcium chloride dihydrate,about 0.2 percent magnesium chloride hexahydrate, and minor amounts ofother salts. As seen from the diagram, a saturated solution of brine intertiary amyl alcohol contains only about 18 percent brine; and asaturated solution of the alcohol in brine contains only about 8 percentalcohol. But in the presence of about 8.3 percent sodium cumenesulfonate, the alcohol and brine become miscible in all proportions.

As noted earlier, however, complete miscibility is not a prerequisite tomiscible displacement. The minimum concentration of sulfonate requiredto achieve miscible displacement of the alcohol by the brine isdetermined by the point at which a line intersects the brine-sulfona'tebase of the diagram, drawn tangent to the plait point of the two-phaseenvelope.

As indicated by the tie lines which dip toward the brine vertex of thediagram, the plait point of this particular envelope lies somewhat tothe left of the peak which corresponds to maximum sulfonateconcentration. Accordingly, the tangent line will intersect thebrinesulfonate base of the diagram at a point corresponding tosubstantially less than 8 percent sulfonate. In practicing theinvention, however, it is generally desirable to inject a brinecontaining substantially more than the minimum concentration ofdetergent, in order to avoid the likelihood that dilution in situ maylower the detergent concentration below the minimum required to achievemiscible displacement.

In the system of FIGURE 3, the brine is the same as that represented inFIGURE 2. As indicated by the diagram, the brine and polar organicphases have substantially less mutual solubility than the correspondingphases of the system of FIGURE 2. As before, however, no more than about8.5 percent sulfonate is required to promote total miscibility betweenthe aqueous and organic phases. An even smaller concentration ofsulfonate would be required to achieve miscible displacement, dependingof course upon the exact location of the plait point as readilydeterminable by routine experimentation.

In the system of FIGURE 4, the efi'ect of salt is demonstrated bycomparing the two-phase envelope of a distilledwater-detergent-pentanoic acid system (Curve I) with that of abrine-detergent-pentanoic acid system (Curve II), wherein the aqueousphase contains about 9.1 percent sodium chloride, about 1.1 percentcalcium chloride dihydrate, about 0.09 percent magnesium chloridehexahydrate, and minor amounts of other salts. It is apparent that thesalt greatly increases the amount of detergent required to achieve totalmiscibility between the aqueous and organic phases. Also, the saltgreatly reduces the solubility of Water in the pentanoic acid, but hassubstantially no effect upon the solubility of pentanoic acid in theaqueous phase.

It does not necessarily follow, however, that the amount of detergentrequired to achieve miscible displacement would be less for distilledwater than for dilute brine. As seen from FIGURE 2, the plait point of abrine systern falls to the left of the two-phase envelope peak, which insome instances may reduce the minimum detergent requirement for dilutebrine compared to that of distilled water.

In each of the above systems represented by FIGURES 1 through 4,detergent concentrations above 25-30 percent by weight may tend to causethe formation of gels. No effort has been made to indicate the exactlocation of a gel envelope on the diagram, since that aspect of thesystem has no direct bearing upon the essential concepts of the presentinvention. However, it is generally advisable to test a proposeddetergent solution, in contact with the polar organic solvent, prior toinjection to determine its suitability as a displacing medium. Aviscosity in excess of cps., for example, is considered too great formost flooding operations, due to reduced injectivities at the inputWells and the consequently excessive periods of time required tocomplete recovery of the oil and the polar organic bank. Preferably, theinjected solutions have a viscosity no greater than 50 cps, andordinarily no greater than 10 cps. at the temperature of injection.

It has been found convenient to approximate the phase behavior of theabove systems in a ternary diagram, even though four or more componentsmay be present. For example, in FIGURE 2 the brine contains asignificant amount of sodium chloride, which is a fourth component ofthe system. This representation is exact only when the ratio ofdissolved salt to water is the same in both phases of any two-phasecomposition. The error introduced by this assumption is relativelyslight, however, and can readily be tolerated in preference to thecomplexity of a three-dimensional four-component phase model,

The invention is further illustrated by the following example:

EXAMPLE I A petroleum reservoir is waterflooded to a residual crude oilsaturation of about 30 percent of the reservoir pore volume. Inaccordance with the present invention, tertiary amyl alcohol is theninjected at a selected number of input wells in an amount correspondingto 5 percent of the total reservoir pore volume. Thereafter, at the sameinput wells, an aqueous detergent solution is injected comprising 15percent sodium xylene sulfonate and 5 percent dissolved inorganic salts.The total amount of injected detergent solution corresponds to 5 percentof the reservoir pore volume. Thereafter, a 30 percent port volume bankof thickened water is injected through the same input wells, containing0.04 percent by weight of partially hydrolyzed polyacrylamide. Thethickened water bank is then followed by water or brine until a total ofabout 1.2 pore volumes of cumulative flooding medium is injected,beginning with the tertiary amyl alcohol. Recovery of reservoir oil andtertiary amyl alcohol is essentially complete from the sections of thereservoir contacted by the injected fluids, indicating miscibledisplacement of each.

A suitable commercial source of oxygenated hydrocarbons, comprising acrude mixture of alcohols, ketones, acids, and aldehydes may be obtainedby the direct catalytic reaction of air or other oxygen-comprising gaswith light paraffinic or olefinic hydrocarbons, such as a lightpetroleum distillate, in accordance with known procedures.

Certain polar organic solvents which are initially miscible withpetroleum, but which lose their ability to miscibly displace thepetroleum upon becoming at least partially saturated with reservoirwater, can be modified to reduce the solubility of water therein, andthereby enable the solvent to retain a sufficient miscibility with thereservoir oil. For example, the addition of 20 percent toluene by weightto tertiary butyl alcohol has been found sufiicient to produce a blendwhich retains its ability to miscibly displace reservoir oil in thepresence of reservoir water, and which also retains its susceptibilityof being miscibly displaced by aqueous detergent solutions.

What is claimed is:

l. A method for the recovery of oil from a subterranean reservoir whichcomprises:

(a) injecting a polar organic solvent into the reservoir;

(b) injecting an aqueous detergent solution into the reservoir, theconcentration of detergent in the solution being at least the minimummiscibility concentration in a system consisting essentially of anaqueous liquid, a polar organic solvent, and a detergent;

(c) displacing the polar organic solvent and the detergent solution inthe reservoir; and

(cl) recovering displaced oil from the reservoir.

2. A method as defined by claim 1 wherein the volume of polar organicsolvent injected is at least 3 percent of the pore volume of thereservoir to be flooded and the volume of the aqueous solution injectedis at least 3 percent of the pore volume of the reservoir to be flooded.

3. A method as defined by claim 2 wherein the polar organic solvent anddetergent solution are displaced by injection of an aqueous solutioninto the reservoir.

4. A method as defined by claim 3 wherein the polar organic solvent isinjected into the reservoir and followed by the detergent solution.

5. A method as defined by claim 2 wherein the polar organic solvent inequilibrium with water is capable of miscibly displacing the reservoiroil, and the detergent solution is capable of miscibly displacing thepolar organic solvent.

6. An improved method for the recovery of oil from a subterraneanreservoir by injecting a polar organic solvent and an aqueous detergentsolution into the reservoir, displacing the polar organic solvent anddetergent solution through the reservoir, and recovering displaced oilfrom the reservoir wherein the detergent, in a system consistingessentially of an aqueous liquid, a polar organic solvent, and adetergent, has a minimum miscibility concenration which is less than thecritical micelle concentration of the detergent in aqueous solution inwhich the improvement comprises injecting a detergent solution having aconcentration of detergent which is greater than the minimum miscibilityconcentration but less than the critical micelle concentration.

References (Cited UNITED STATES PATENTS 2,742,089 4/1956 Morse et al.1669 2,827,964 3/1958 Sandiford et al. 166-9 3,076,504 2/1963 Meadors etal. 166-9 3,079,336 2/1963 Stright et al. l66-9 X 3,266,570 8/1966Gogarty 166-9 3,323,588 6/1967 Rai et al. 166-9 3,330,344 7/1967Reisberg 166-9 3,330,345 7/1967 Henderson et al. 1669 3,366,174 1/1968Ferrell et a1. l66-9 STEPHEN J. NOVOSAD, Primary Examiner.

US. Cl. X.R. 252-855

